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  • clear explanation sought: throw() and stack unwinding

    - by Jerry Gagelman
    I'm not a programmer but have learned a lot watching others. I am writing wrapper classes to simplify things with a really technical API that I'm working with. Its routines return error codes, and I have a function that converts those to strings: static const char* LibErrString(int errno); For uniformity I decided to have member of my classes throw an exception when an error is encountered. I created a class: struct MyExcept : public std::exception { const char* errstr_; const char* what() const throw() {return errstr_;} MyExcept(const char* errstr) : errstr_(errstr) {} }; Then, in one of my classes: class Foo { public: void bar() { int err = SomeAPIRoutine(...); if (err != SUCCESS) throw MyExcept(LibErrString(err)); // otherwise... } }; The whole thing works perfectly: if SomeAPIRoutine returns an error, a try-catch block around the call to Foo::bar catches a standard exception with the correct error string in what(). Then I wanted the member to give more information: void Foo::bar() { char adieu[128]; int err = SomeAPIRoutine(...); if (err != SUCCESS) { std::strcpy(adieu,"In Foo::bar... "); std::strcat(adieu,LibErrString(err)); throw MyExcept((const char*)adieu); } // otherwise... } However, when SomeAPIRoutine returns an error, the what() string returned by the exception contains only garbage. It occurred to me that the problem could be due to adieu going out of scope once the throw is called. I changed the code by moving adieu out of the member definition and making it an attribute of the class Foo. After this, the whole thing worked perfectly: a try-call block around a call to Foo::bar that catches an exception has the correct (expanded) string in what(). Finally, my question: what exactly is popped off the stack (in sequence) when the exception is thrown in the if-block when the stack "unwinds?" As I mentioned above, I'm a mathematician, not a programmer. I could use a really lucid explanation of what goes onto the stack (in sequence) when this C++ gets converted into running machine code.

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  • multiple valgrind errors: Conditional jump or move depends on uninitialised value(s)

    - by Hristo
    I'm running valgrind and I'm getting the following error (this is not the only one): ==21743== Conditional jump or move depends on uninitialised value(s) ==21743== at 0x4A06509: index (mc_replace_strmem.c:164) ==21743== by 0x33B7CBB3CD: gaih_inet (in /lib64/libc-2.5.so) ==21743== by 0x33B7CBD629: getaddrinfo (in /lib64/libc-2.5.so) ==21743== by 0x401A5F: tunnelURL (proxy.c:336) ==21743== by 0x40142A: client_thread (proxy.c:194) ==21743== by 0x33B8806616: start_thread (in /lib64/libpthread-2.5.so) ==21743== by 0x33B7CD3C2C: clone (in /lib64/libc-2.5.so) My tunnelURL() function looks like this: char * tunnelURL(char *url) { char * a = strstr(url, "//"); a += 2; char * path = strstr(a, "/"); char host[256]; strncpy (host, a, strlen(a)-strlen(path)); /* * The following is courtesy of Beej's Guide */ int status; int proxySocketFD; struct addrinfo hints; struct addrinfo *servinfo; // will point to the results memset(&hints, 0, sizeof(hints)); // make sure the struct is empty hints.ai_family = AF_INET; // don't care IPv4 or IPv6 hints.ai_socktype = SOCK_STREAM; // TCP stream sockets hints.ai_flags = AI_PASSIVE; // fill in my IP for me if ((status = getaddrinfo(host, "80", &hints, &servinfo)) != 0) { perror("getaddrinfo() fail"); exit(1); } // create socket if ((proxySocketFD = socket(servinfo->ai_family, servinfo->ai_socktype, servinfo->ai_protocol)) == -1) { perror("proxy socket() fail"); exit(1); } // connect if (connect(proxySocketFD, servinfo->ai_addr, servinfo->ai_addrlen) != 0) { printf("connect() fail"); exit(1); } // construct request char request[strlen(path) + strlen(host) + 26]; sprintf(request, "GET %s HTTP/1.1\r\nHost: %s\r\n\r\n", path, host); printf("%s", request); // send request send(proxySocketFD, request, strlen(request), 0); // receive response int i = 0; int amntRecvd = 0; char *pageContentBuffer = (char*) malloc(4096 * sizeof(char)); while ((amntRecvd = recv(proxySocketFD, pageContentBuffer + i, 4096, 0)) > 0) { i += amntRecvd; realloc(pageContentBuffer, i * 4096 * sizeof(char)); } // close proxy socket close(proxySocketFD); // deallocate memory freeaddrinfo(servinfo); return pageContentBuffer; } Line 336 corresponds to the if statement with the getaddrinfo() function call. I'm not really sure what I haven't initialized. The string I'm passing in "should" be already set... I'm printing it out just fine. I also get another error corresponding to the same line of code: ==21743== Use of uninitialised value of size 8 ==21743== at 0x33B7D05816: __nscd_cache_search (in /lib64/libc-2.5.so) ==21743== by 0x33B7D0438B: nscd_gethst_r (in /lib64/libc-2.5.so) ==21743== by 0x33B7D04B26: __nscd_gethostbyname2_r (in /lib64/libc-2.5.so) ==21743== by 0x33B7CE9F5E: gethostbyname2_r@@GLIBC_2.2.5 (in /lib64/libc-2.5.so) ==21743== by 0x33B7CBC522: gaih_inet (in /lib64/libc-2.5.so) ==21743== by 0x33B7CBD629: getaddrinfo (in /lib64/libc-2.5.so) ==21743== by 0x401A5F: tunnelURL (proxy.c:336) ==21743== by 0x40142A: client_thread (proxy.c:194) ==21743== by 0x33B8806616: start_thread (in /lib64/libpthread-2.5.so) ==21743== by 0x33B7CD3C2C: clone (in /lib64/libc-2.5.so) Any ideas as to what might becausing this? This is written in C btw... Thanks, Hristo

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  • Sybase: how can I remove non-printable characters from CHAR or VARCHAR fields with SQL?

    - by Kenny Drobnack
    I'm working with a Sybase database that seems to have non-printable characters in some of the string fields and this is throwing off some of our processing code. At first glance, it seemed to only be newlines and carriage returns, but we also have an ASCII code 27 in there - an ESC character, some accented characters, and some other oddities in there. I have no direct access to change the database, so changing the bad data isn't an option, yet. For now I have to make do with just filtering it out. We're trying to export the table data from one database and load it into a database used by another application in a nightly batch process. Ideally, I'd like to have a function that I can pass a list of characters and just have Sybase return the data with those characters removed. I'd like to keep it something we could do in plain SQL if possible. Something like this to remove characters that are ASCII 0 - 31. select str_replace(FIELD1, (0-31), NULL) as FIELD1, str_replace(FIELD2, (0-31), NULL) as FIELD2 from TABLE So far, str_replace is the nearest I can find, but it only allows replacing one string with another. No support for character ranges and won't let me do the above. We're running on Sybase ASE 12.5 on Unix servers.

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  • Can the csv format be defined by a regex?

    - by Spencer Rathbun
    A colleague and I have recently argued over whether a pure regex is capable of fully encapsulating the csv format, such that it is capable of parsing all files with any given escape char, quote char, and separator char. The regex need not be capable of changing these chars after creation, but it must not fail on any other edge case. I have argued that this is impossible for just a tokenizer. The only regex that might be able to do this is a very complex PCRE style that moves beyond just tokenizing. I am looking for something along the lines of: ... the csv format is a context free grammar and as such, it is impossible to parse with regex alone ... Or am I wrong? Is it possible to parse csv with just a POSIX regex? For example, if both the escape char and the quote char are ", then these two lines are valid csv: """this is a test.""","" "and he said,""What will be, will be."", to which I replied, ""Surely not!""","moving on to the next field here..."

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  • String Question. How to count the number of A,a, numeric and special char

    - by Brad
    I have randomly created strings such as H*P2[-%-3:5RW0j*;k52vedsSQ5{)ROkb]P/*DZTr*-UX4sp What I want to do is get a count of all Caps, lower case, numeric and special characters in each string as they are generated. I am looking for an output similar to Caps = 5 Lower = 3 numneric = 6 Special = 4 Fictitious values of course. I have gone through the php string pages using count_char, substr_count etc but cant find what I am looking for. Thank you

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  • How is precedence determined in C pointers?

    - by ankur.trapasiya
    I've come across two pointer declarations that I'm having trouble understanding. My understanding of precedence rules goes something like this: Operator Precedence Associativity (), [ ] 1 Left to Right *, identifier 2 Right to Left Data type 3 But even given this, I can't seem to figure out how to evaluate the following examples correctly: First example float * (* (*ptr)(int))(double **,char c) My evaluation: *(ptr) (int) *(*ptr)(int) *(*(*ptr)(int)) Then, double ** char c Second example unsigned **( * (*ptr) [5] ) (char const *,int *) *(ptr) [5] *(*ptr)[5] *(*(*ptr)[5]) **(*(*ptr)[5]) How should I read them?

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  • C++ simple arrays and pointers question

    - by nashmaniac
    So here's the confusion, let's say I declare an array of characters char name[3] = "Sam"; and then I declare another array but this time using pointers char * name = "Sam"; What's the difference between the two? I mean they work the same way in a program. Also how does the latter store the size of the stuff that someone puts in it, in this case 3 characters? Also how is it different from char * name = new char[3]; If those three are different where should they be used I mean in what circumstances?

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  • Index independent character comparison within text blocks

    - by Michael IV
    I have the following task: developing a program where there is a block of sample text which should be typed by user. Any typos the user does during the test are registered. Basically, I can compare each typed char with the sample char based on caret index position of the input, but there is one significant flaw in such a "naive" approach. If the user typed mistakenly more letters than a whole string has, or inserted more white spaces between the string than should be, then the rest of the comparisons will be wrong because of the index offsets added by the additional wrong insertions. I have thought of designing some kind of parser where each string (or even a char ) is tokenized and the comparisons are made "char-wise" and not "index-wise," but that seems to me like an overkill for such a task. I would like to get a reference to possibly existing algorithms which can be helpful in solving this kind of problem.

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  • Is it safe to convert varchar and char into nvarchar and nchar in SQL Server?

    - by Svish
    We currently have a number of columns in the database which are of type varchar. The application that uses them are in C# and it uses Linq2Sql for the communication (or what to call it). We would like to support unicode characters, which means we would have to convert the varchar columns into nvarchar. Is this a safe operation? Is it just a matter of changing the column type and updating the dbml file, or are there more stuff that needs to be done? Any changes in the C# code? Do I need to somehow convert the text that already exist in the database manually, or is it handled for me?

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  • Given a string of letters from alphabet insert frequency of each character in the string.in O(n) time and O(1) space [on hold]

    - by learner
    Below is my attempt void str_freq(char *str, int len) { char c; int cnt=0; c=str[0]; int i,j=0; for(i=0;i<len;i++) { if(c==str[i]) { cnt++; } else { c = str[i]; // printf(" %d ",cnt); str[j] = str[i-1]; str[j+1] = (char)(((int)'0')+cnt); j++; cnt=0; } } str[j+1]='\0'; printf("%s",str); } int main() { char str[] = "aaabbccccdeffgggg"; int length=strlen(str); str_freq(str,length); } I am getting wrong answer abcdef1 instead of a3b2c4d1e1f2g4. Please let me know where I am going wrong.

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  • Gettings Terms asscoiated to a Specific list item

    - by Gino Abraham
    I had a fancy requirement where i had to get all tags associated to a document set in a document library. The normal tag could webpart was not working when i add it to the document set home page, so planned a custom webpart. Was checking in net to find a straight forward way to achieve this, but was not lucky enough to get something. Since i didnt get any samples in net, i looked into Microsoft.Sharerpoint.Portal.Webcontrols and found a solution.The socialdataframemanager control in 14Hive/Template/layouts/SocialDataFrame.aspx directed me to the solution. You can get the dll from ISAPI folder. Following Code snippet can get all Terms associated to the List Item given that you have list name and id for the list item. using System; using System.Collections.Generic; using System.Linq; using System.Text; using Microsoft.SharePoint; using Microsoft.Office.Server.SocialData; namespace TagChecker { class Program { static void Main(string[] args) { // Your site url string siteUrl = http://contoso; // List Name string listName = "DocumentLibrary1"; // List Item Id for which you want to get all terms int listItemId = 35; using (SPSite site = new SPSite(siteUrl)) { using(SPWeb web = site.OpenWeb()) { SPListItem listItem = web.Lists[listName].GetItemById(listItemId); string url = string.Empty; // Based on the list type the url would be formed. Code Sniffed from Micosoft dlls :) if (listItem.ParentList.BaseType == SPBaseType.DocumentLibrary) { url = listItem.Web.Url.TrimEnd(new char[] { '/' }) + "/" + listItem.Url.TrimStart(new char[] { '/' }); } else if (SPFileSystemObjectType.Folder == listItem.FileSystemObjectType) { url = listItem.Web.Url.TrimEnd(new char[] { '/' }) + "/" + listItem.Folder.Url.TrimStart(new char[] { '/' }); } else { url = listItem.Web.Url.TrimEnd(new char[] { '/' }) + "/" + listItem.ParentList.Forms[PAGETYPE.PAGE_DISPLAYFORM].Url.TrimStart(new char[] { '/' }) + "?ID=" + listItem.ID.ToString(); } SPServiceContext serviceContext = SPServiceContext.GetContext(site); Uri uri = new Uri(url); SocialTagManager mgr = new SocialTagManager(serviceContext); SocialTerm[] terms = mgr.GetTerms(uri); foreach (SocialTerm term in terms) { Console.WriteLine(term.Term.Labels[0].Value ); } } } Console.Read(); } } } Reference dlls added are Microsoft.Sharepoint , Microsoft.Sharepoint.Taxonomy, Microsoft.office.server, Microsoft.Office.Server.UserProfiles from ISAPI folder. This logic can be used to make a custom tag cloud webpart by taking code from OOB tag cloud, so taht you can have you webpart anywhere in the site and still get Tags added to a specifc libdary/List. Hope this helps some one.

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  • failbit is being set and I can't figure out why

    - by felipedrl
    I'm writing a MIDI file loader. Everything is going fine until at some track I get a failbit exception while trying to read from file. I can't figure out why, I've checked the file size and it's ok too. Upon checking "errno" and it returns "0". Any ideas? Thanks. The snippet follows: file.read(reinterpret_cast<char*>(&mHeader.id), sizeof(MidiHeader)); mTracks = new MidiTrack[mHeader.nTracks]; for (uint i = 0; i < mHeader.nTracks; ++i) { // this read fails on 6th i. I've checked hexadecimal file and it's // ok so far. file.read(reinterpret_cast<char*>(&mTracks[i].id), sizeof(uint)); if (file.fail()) { std::cerr << errno << std::endl; massert(false); } massert(mTracks[i].id == 0x6B72544D); file.read(reinterpret_cast<char*>(&mTracks[i].size), sizeof(uint)); mTracks[i].size = swapBytes(mTracks[i].size); mTracks[i].data = new char[mTracks[i].size]; file.read(mTracks[i].data, mTracks[i].size * sizeof(char)); totalBytesRead += 8 + mTracks[i].size; massert(totalBytesRead <= fileSize); }

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  • Why does TrimStart trims a char more when asked to trim "PRN.NUL" ?

    - by James
    Here is the code: namespace TrimTest { class Program { static void Main(string[] args) { string ToTrim = "PRN.NUL"; Console.WriteLine(ToTrim); string Trimmed = ToTrim.TrimStart("PRN.".ToCharArray()); Console.WriteLine(Trimmed); ToTrim = "PRN.AUX"; Console.WriteLine(ToTrim); Trimmed = ToTrim.TrimStart("PRN.".ToCharArray()); Console.WriteLine(Trimmed); ToTrim = "AUX.NUL"; Console.WriteLine(ToTrim); Trimmed = ToTrim.TrimStart("AUX.".ToCharArray()); Console.WriteLine(Trimmed); } } } The output is like this: PRN.NUL UL PRN.AUX AUX AUX.NUL NUL As you can see, the TrimStart took out the N from NUL. But it doesn't do that for other strings even if it started with PRN. I tried with .NET Framework 3.5 and 4.0 and the results are same. Are there any explanation on what causes this behavior?

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  • Linked Lists in Java - Help with assignment

    - by doron2010
    I have been trying to solve this assignment all day, please help me. I'm completely lost. Representation of a string in linked lists In every intersection in the list there will be 3 fields : The letter itself. The number of times it appears consecutively. A pointer to the next intersection in the list. The following class CharNode represents a intersection in the list : public class CharNode { private char _data; private int _value; private charNode _next; public CharNode (char c, int val, charNode n) { _data = c; _value = val; _next = n; } public charNode getNext() { return _next; } public void setNext (charNode node) { _next = node; } public int getValue() { return _value; } public void setValue (int v) { value = v; } public char getData() { return _data; } public void setData (char c) { _data = c; } } The class StringList represents the whole list : public class StringList { private charNode _head; public StringList() { _head = null; } public StringList (CharNode node) { _head = node; } } Add methods to the class StringList according to the details : (Pay attention, these are methods from the class String and we want to fulfill them by the representation of a string by a list as explained above) public char charAt (int i) - returns the char in the place i in the string. Assume that the value of i is in the right range. public StringList concat (String str) - returns a string that consists of the string that it is operated on and in its end the string "str" is concatenated. public int indexOf (int ch) - returns the index in the string it is operated on of the first appeareance of the char "ch". If the char "ch" doesn't appear in the string, returns -1. If the value of fromIndex isn't in the range, returns -1. public int indexOf (int ch, int fromIndex) - returns the index in the string it is operated on of the first appeareance of the char "ch", as the search begins in the index "fromIndex". If the char "ch" doesn't appear in the string, returns -1. public boolean equals (String str) - returns true if the string that it is operated on is equal to the string str. Otherwise returns false. This method must be written in recursion, without using loops at all. public int compareTo (String str) - compares between the string that the method is operated on to the string "str" that is in the parameter. The method returns 0 if the strings are equal. If the string in the object is smaller lexicographic from the string "str" in the paramater, a negative number will be returned. And if the string in the object is bigger lexicographic from the string "str", a positive number will be returned. public StringList substring (int i) - returns the list of the substring that starts in the place i in the string on which it operates. Meaning, the sub-string from the place i until the end of the string. Assume the value of i is in the right range. public StringList substring (int i, int j) - returns the list of the substring that begins in the place i and ends in the place j (not included) in the string it operates on. Assume the values of i, j are in the right range. public int length() - will return the length of the string on which it operates. Pay attention to all the possible error cases. Write what is the time complexity and space complexity of every method that you wrote. Make sure the methods you wrote are effective. It is NOT allowed to use ready classes of Java. It is NOT allowed to move to string and use string operations.

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  • when should a database table be broken into multiple tables with relations?

    - by GSto
    I have an application that needs to store client data, and part of that is some data about their employer as well. Assuming that a client can only have one employer, and that the chance of people having identical employer data is slim to none, which schema would make more sense to use? Schema 1 Client Table: ------------------- id int name varchar(255), email varchar(255), address varchar(255), city varchar(255), state char(2), zip varchar(16), employer_name varchar(255), employer_phone varchar(255), employer_address varchar(255), employer_city varchar(255), employer_state char(2), employer_zip varchar(16) **Schema 2** Client Table ------------------ id int name varchar(255), email varchar(255), address varchar(255), city varchar(255), state char(2), zip varchar(16), Employer Table --------------------- id int name varchar(255), phone varchar(255), address varchar(255), city varchar(255), state char(2), zip varchar(16) patient_id int Part of me thinks that since are clearly two different 'objects' in the real world, seperating them out into two different tables makes sense. However, since a client will always have an employer, I'm also not seeing any real benefits to seperating them out, and it would make querying data about clients more complex. Is there any benefit / reason for creating two tables in a situation like this one instead of one?

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  • where is the error in this C code , and how to get rid of the warnings?

    - by mekasperasky
    #include<stdio.h> #include<string.h> //This program is a sorting application that reads a sequence of numbers from a file and prints them on the screen . The reading from the file here , is a call back function . typedef int (*CompFunc)(const char* , const char* ); typedef int (*ReadCheck)(char nullcheck); char array[100]; //Let this fucntion be done in the library itself . It doesnt care as to where the compare function and how is it implemented . Meaning suppose the function wants to do sort in ascending order or in descending order then the changes have to be done by the client code in the "COMPARE" function who will be implementing the lib code . void ReadFile(FILE *fp,ReadCheck rc) { char a; char d[100]; int count = 0,count1=0; a=fgetc(fp); while(1 != (*rc)(a)) { if(a=='\0') { strcpy(array[count],d); count=count+1; } else { d[count1]=a; count1=count1+1; } } } void Bubblesort(int* array , int size , int elem_size , CompFunc cf) { int i,j; int *temp; for( i=0;i < size ;i++) { for ( j=0;j < size -1 ; j++) { // make the callback to the comparision function if(1 == (*cf)(array+j*elem_size,array+ (j+1)*elem_size)) { //interchanging of elements temp = malloc(sizeof(int *) * elem_size); memcpy(temp , array+j*elem_size,elem_size); memcpy(array+j*elem_size,array+(j+1)*elem_size,elem_size); memcpy(array + (j+1)*elem_size , temp , elem_size); free(temp); } } } } //Let these functions be done at the client side int Compare(const char* el1 , const char* el2) { int element1 = *(int*)el1; int element2 = *(int*)el2; if(element1 < element2 ) return -1; if(element1 > element2) return 1 ; return 0; } int ReadChecked(char nullcheck) { if (nullcheck=='\n') return 1; else return 0; } int main() { FILE fp1; int k; fp1=fopen("readdata.txt","r"); Readfile(fp1,&ReadChecked); Bubblesort((char*)array,5,sizeof(array[0]),&Compare); printf("after sorting \n"); for (k=0;k<5;k++) printf("%d",array[k]); return 0; } The error i get is fsc1.c: In function ‘ReadFile’: fsc1.c:19: warning: passing argument 1 of ‘strcpy’ makes pointer from integer without a cast fsc1.c: In function ‘Bubblesort’: fsc1.c:40: warning: passing argument 1 of ‘cf’ from incompatible pointer type fsc1.c:40: warning: passing argument 2 of ‘cf’ from incompatible pointer type fsc1.c:43: warning: incompatible implicit declaration of built-in function ‘malloc’ fsc1.c:47: warning: incompatible implicit declaration of built-in function ‘free’ fsc1.c: In function ‘main’: fsc1.c:80: error: incompatible types in assignment fsc1.c:82: warning: passing argument 1 of ‘Bubblesort’ from incompatible pointer type

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  • Override methods should call base method?

    - by Trevor Pilley
    I'm just running NDepend against some code that I have written and one of the warnings is Overrides of Method() should call base.Method(). The places this occurs are where I have a base class which has virtual properties and methods with default behaviour but which can be overridden by a class which inherits from the base class and doesn't call the overridden method. For example, in the base class I have a property defined like this: protected virtual char CloseQuote { get { return '"'; } } And then in an inheriting class which uses a different close quote: protected override char CloseQuote { get { return ']'; } } Not all classes which inherit from the base class use different quote characters hence my initial design. The alternatives I thought of were have get/set properties in the base class with the defaults set in the constructor: protected BaseClass() { this.CloseQuote = '"'; } protected char CloseQuote { get; set; } public InheritingClass() { this.CloseQuote = ']'; } Or make the base class require the values as constructor args: protected BaseClass(char closeQuote, ...) { this.CloseQuote = '"'; } protected char CloseQuote { get; private set; } public InheritingClass() base (closeQuote: ']', ...) { } Should I use virtual in a scenario where the base implementation may be replaced instead of extended or should I opt for one of the alternatives I thought of? If so, which would be preferable and why?

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  • C++: Get char after space character instead or return carriage.

    - by Kzone272
    Okay this is similar to my last question but what I ended up doing was way too complex for something as simple as this. I simply need to get a single character or number (I will know which of these I am receiving) from the console after I press space, instead of pressing enter. I'm sure there must be a way to have the terminal read input after a space instead of a '\n'. I need to read inputs from the console in which the succeeding data types will vary depending on what the first input is, and I think reading the entire line, parsing it into strings, then parsing some of those into ints is a bit unnecessary. So Is this actually not possible in C++ or have I just not found it yet?

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